The present invention relates to radio utility meter reading processing, and is more particularly but not exclusively concerned with a radio transmitter antenna arrangement which is associated with a utility meter, particularly a water meter, for the purpose of transmitting readings of such meter from a generally underground pit box to a remote receiver.
In conventional practice in the area of utility meter reading for data acquisition and automatic billing, a meter which is intended to be remotely read is installed with a radio transmitter. Such radio transmitter produces radio frequency energy that is coupled to an antenna for broadcasting.
Generally, the nature of such arrangements results in the antenna being placed in an outdoor environment, often at ground level, and in close proximity to a variety of materials and varying weather conditions. Nearby materials may include (and may change from time to time, depending on the environment) items such as metal, plastic, concrete, or organic materials. Weather conditions may involve, from time to time, environmental exposure to ice, snow, water, and temperature extremes (both cold and hot).
The amount of radio frequency energy actually irradiated into the airwaves as compared with that intended to be irradiated is a function of a number of factors. Such factors may include the applied voltage, the amount of current flowing through the antenna, the frequency of the signal applied to the antenna, the material from which the antenna is made, the geometry of such antenna, and the materials that are in a relatively close surrounding space of the antenna (such as within a sphere-radius measuring up to a few wavelengths of the radio signal applied to such antenna). When the surroundings of the antenna vary, the antenna performance (ie., the degree of the radiated energy therefrom) will also tend to vary correspondingly. The more that adjacent or nearby materials tend to permeate the environment of a particular antenna, the greater the affects on the antenna and its performance, typically to the detriment of such performance.
As is well known, current flow is a function of applied voltage and the equivalent impedance of the system. The equivalent impedance system for an antenna generally is a function of the efficiency of the antenna itself, of the impedance characteristics of the transmission line which is carrying the radio frequency energy from a transmitter to such antenna, and of the geometry of such antenna that presents a particular impedance at given frequencies of operation.
To achieve desired range and reliability of radio frequency communications from pit box generated data, it would be desirable to maintain a controlled and also uniform radio frequency energy irradiation pattern from the antenna used to transmit a radio signal from an enclosed utility meter. One type of antenna conventionally used for utility meter remote transmitting uses a conventional loop antenna design as the irradiator element. Generally speaking, the proximity to the ground which is required for the arrangement results in a deformation in the irradiation pattern produced by the irradiated signal.
Problems encountered with such non-uniform irradiation patterns are further complicated by the fact that irradiated energy may vary from place to place where the antenna is installed. For example, in some antenna systems there may be multiple transmitters that will be sending data to a receiver system, where the transmitter antenna will be installed in cast iron, plastic, or concrete lids of boxes installed underground and with lids thereof generally flush with ground level. Such boxes are commonly called pit boxes in the utility industry, particularly in the water utility industry.
A number of attempts have been made to provide an antenna system that is capable of operating in particular from a water meter pit box environment. However, complete systems for water meters on occasion have been required to be removed from the field for reasons such as poor antenna function, poor range, inconsistent range, and other related problems that also affect the life and/or durability of the effective water meter reading system using a radio frequency transmitter system for data collection.
A number of factors are subject to consideration in providing any successful integrated antenna system. A few of such conditions or factors may include: frequency of operation, transmitter output power, antenna gain, antenna polarization, antenna pattern, azimuth beam-width, azimuth variation, government regulations for operating radio equipment, characteristic antenna impedance, coefficient of maximum wave reflection, antenna geometry, antenna location, ability to effect installation, length of service life desired, ability to operate in exposed environmental conditions such as exposure to water with only very small variation in operation performance due to any water absorption into the antenna system, ultra-violet resistance, shock and vibration resistance, and environmental temperature variability resistance. At the same time, one must be aware of cost factors and the ability to manufacture a large volume of such units (for use in a full system having a number of meter reading locations) with reliability and repeatability of performance.
Examples of several known antenna arrangements for use with utility meter pit boxes are disclosed in Cerny, et al. (U.S. Pat. No. 5,298,894) and Meek, et al. (U.S. Pat. No. 5,621,419). The complete disclosures of such patents are fully incorporated herein by reference.